Molar activity of [18F]FP-(+)-DTBZ radiopharmaceutical: Determination and its effect on quantitative analysis of VMAT2 autoradiography

[ 18 F]fluoropropyl-(+)-dihydrotetrabenazine ([ 18 F]FP-(+)-DTBZ) is a rising positron tracer for imaging vesicular monoamine transporter II (VMAT2) in the central nervous system. The present work was to develop a novel chromatographic method capable of the molar activity (A m ) determination of [ 18 F]FP-(+)-DTBZ. As a complement work of the A m measurement, we also investigated the effect of A m on the quantitative analysis of VMAT2 autoradiography with [ 18 F]FP-(+)-DTBZ. The A m determination was performed by high performance liquid chromatography (HPLC) using the non-radioactive standard (FP-(+)-DTBZ) for calibration plot of peak area against concentration. Based on this correlation, the A m of [ 18 F]FP-(+)-DTBZ was calculated and corrected to the end of synthesis. In the quantitative analysis of in vitro VMAT2 autoradiography, the striatum radioactivity uptake together with the uptake ratio of striatum versus cortex reduced along with the decrease of A m and the increase of the FP-(+)-DTBZ content. Therefore, the A m and the corresponding FP-(+)-DTBZ content have a significant effect on the quantitative analysis of VMAT2 autoradiography using [ 18 F]FP-(+)-DTBZ.